BACKGROUND & NATURE OF THE CASE NAT'L STEEL CORP IS A DELAWARE CORP WITH HEADQUARTERS IN PITTSBURGH. NAT'L OWNS & OPERATES A FULLY INTEGRATED IRON & STEEL MILL AT TWO ADJACENT LOCATIONS NEAR DETROIT. PARTS OF THE FACILITY, KNOWN AS GREAT LAKES STEEL, ARE LOCATED AT ECORSE & ZUG ISLAND IN SOURTHERN WAYNE COUNTY, MI. THE FACILITIES ARE LOCATED IN AREAS NOT MEETING THE PRIMARY AMBIENT AIR QUALITY STANDARDS FOR PARTICULATE MATTER. THE COURT ORDER INITIALLY (3/31/81) REQUIRED THAT NAT'L STELL CORP INSTALL POSITIVE POLLUTION CONTROL EQUIPMENT ON EACH OF ITS FOUR BLAST FURNACE CASTHOUSES ON VARYING SCHED- ULES ENDING WITH THE REQUIREMENT TO ACHIEVE AND DEMONSTRATE COMPLIANCE ON 6/30/82, FOR THE FIRST AND 12/31/82, FOR THE LAST. IN ADDITION, THE ORIGINAL ORDER REQUIRED THAT NAT'L STEEL INSTALL HOODING AND GAS CLEANING DEVICES TO CAPTURE & COLLECT SECONDARY EMISSIONS FROM THE #1 & #2 BOF SHOPS BY 10/31/82 AND 11/15/82, RESPECTIVELY. IN LATE 1981 NAT'L STEEL SUBMITTED A SIP REVISION TO THE STATE OF MI WHICH WOULD ELIMINATE THE REQUIREMENTS TO CONTROL SECONDARY EMIS- SIONS FROM THE #2 BOF SHOP, PROVIDE FOR CLOSING THE #1 BOF, AND ELIMINATE THE REQUIREMENTS TO CONTROL BLAST FURNACE CASTHOUSE EMISSIONS. IN LIEU OF THESE REQUIREMENTS, THE REVISION SUBSTITUTED CONTROLS EXCEEDING THE LEVELS REQUIRED BY RACT ON ROADS AND OTHER SOURCES OF FUGITIVE DUST & OVER- CONTROL AT THE ELECTRIC ARC FURNACE SHOP.